bridge: remove rtmsg_ifinfo called in add_del_if

Since commit dc709f37 ("rtnetlink: bring NETDEV_CHANGEUPPER event
process back in rtnetlink_event"), rtnetlink_event would process the
NETDEV_CHANGEUPPER event and send a notification to userspace.

In add_del_if, it would generate NETDEV_CHANGEUPPER event by whether
netdev_master_upper_dev_link or netdev_upper_dev_unlink. There's
no need to call rtmsg_ifinfo to send the notification any more.

So this patch is to remove it from add_del_if also to avoid redundant
notifications.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>